When a semicrystalline polyaryletherketone filament is specified for fused filament fabrication of parts exposed to hot water, steam, or hydrocarbon environments, the Ensinger TECAFIL PEEK VX black filament in 1.75 mm diameter is positioned as an unfilled, black-pigmented polyetheretherketone feedstock. The grade is not a carbon-fibre-reinforced compound; the black colour is derived from pigmentation rather than chopped carbon fibre. Manufacturer-published bulk resin data for unfilled PEEK of this class include density of 1.32 g/cm³ under ISO 1183-1, a melting peak of 343 °C under ISO 11357-3, and glass transition temperature of 143 °C under ISO 11357-2. The filament format is intended for high-temperature fused filament fabrication systems with all-metal hot ends and actively heated build chambers that can be maintained above 400 °C and 120 °C respectively.

Drying is a processing prerequisite, not a recommendation. PEEK absorbs approximately 0.3 % to 0.5 % moisture at saturation, and residual moisture above 0.02 % can hydrolyse the melt at processing temperatures above 340 °C, producing voids, rough extrudate, and delamination at layer interfaces. The filament should be dried at 150 °C for 3 h in a dry-air or vacuum dryer with a dew point of −40 °C or lower, or at 120 °C for 5 h where dryer capacity limits batch throughput. Storage in sealed containers with desiccant is required when ambient relative humidity exceeds 60 %. Production lines use residual moisture analysers to confirm moisture content before extrusion because batch-to-batch variation in dampness alters melt viscosity and extrusion pressure.

Extrusion of the 1.75 mm filament requires an all-metal hot end with a hardened steel or high-temperature plated copper alloy nozzle, a PT1000 or thermocouple sensor rated for 450 °C, and a melt path free of PTFE or polyimide liners. Typical processing windows for unfilled PEEK filaments are nozzle temperature 400–430 °C, bed temperature 160–200 °C, chamber temperature 120–180 °C, and print speed 20–50 mm/s. Layer heights of 0.10–0.20 mm are common. The supplier-published diameter tolerance for engineering filaments is commonly ±0.05 mm, which is necessary for stable feed force when paired with a dual-drive extruder and a constrained filament path. Cooling fans should remain off or below 20 % duty cycle to avoid quenching the melt before sufficient interlayer diffusion has occurred.

Processing Constraints in Heated-Chamber FFF of TECAFIL PEEK VX Black

In a chamber held below 120 °C, deposited PEEK cools into a low-crystallinity state, leaving frozen-in orientation and residual stress that manifests as corner lift, vertical warping, and interlayer fracture. The crystallisation window for PEEK lies between the glass transition at 143 °C and the melt peak at 343 °C; practical crystallisation rates are highest between 180 °C and 280 °C. When chamber air temperature is maintained above 150 °C, printed weld interfaces retain chain mobility long enough for partial co-crystallisation across the layer boundary. On an open-frame printer without an actively heated chamber, warpage on parts exceeding 100 mm in the longest axis is frequently observed even with polyimide tape adhesion and a high bed setpoint. This behaviour restricts production-scale PEEK fused filament fabrication to systems with heated chambers certified for continuous operation at 200 °C.

The table represents unfilled PEEK resin data and is not a guarantee of printed-part values. Print orientation, raster angle, chamber temperature, and annealing history shift tensile strength and elongation. Published data for TECAFIL PEEK VX black in all printed orientations are limited; qualification coupons should therefore be produced with the same raster sequence and post-annealing history as production components and tested under ISO 527-2 and ISO 178.

Fused filament fabrication with 1.75 mm unfilled PEEK produces visible layer lines and local porosity that act as stress concentrators. Z-direction tensile properties are commonly 30–60 % lower than in-plane values because interlayer welding is incomplete compared with bulk resin. Annealing at 200 °C for 2 h in an air-circulating oven increases crystallinity and reduces residual stress, but it can produce dimensional change of up to 1–2 % in the build direction. Machining, polishing, or chemical smoothing is often required for sealing surfaces. PEEK printed parts also absorb moisture after printing, so dry storage in desiccating cabinets is recommended when tight dielectric or mechanical tolerances are required.

Where Unfilled VX Black Diverges from Carbon-Fibre and Glass-Fibre PEEK Filaments

Compared with a carbon-fibre-filled PEEK filament of identical diameter, the unfilled VX black grade exhibits lower modulus, higher elongation at break, reduced nozzle wear, and higher electrical resistivity. Carbon-fibre-filled PEEK typically shifts tensile modulus from the 4,200 MPa class toward 10,000–14,000 MPa, but it also lowers elongation and introduces anisotropic shrinkage and conductive paths. Glass-fibre-filled PEEK increases stiffness and creep resistance but reduces ductility and can create abrasive wear on brass or hardened steel nozzles. The unfilled grade retains the dielectric behaviour of neat PEEK, with volume resistivity commonly above 10¹⁵ Ω·cm under IEC 62631-3-1, whereas carbon-fibre-filled grades may fall below 10⁴ Ω·cm depending on fibre loading. In applications requiring electrical insulation, low particle shedding, and ductile failure under tensile load, the unfilled VX black is specified over carbon-fibre-filled formulations.

The black pigmentation should not be mistaken for carbon-fibre reinforcement. The grade is unfilled; the pigment reduces light transmission but does not provide the mechanical reinforcement of chopped-carbon-fibre PEEK. In UV-exposed or light-sensitive applications, long-term stability should be verified under ISO 4892-2 or ASTM G154 because polyetheretherketone can undergo surface oxidation and chalking without stabilisers.

Compared with polyetherimide filaments such as ULTEM 1010, unfilled PEEK VX black has a higher continuous use temperature, better resistance to steam and many solvents, and higher abrasion resistance. However, polyetherimide is processable at lower nozzle temperatures of 360–380 °C and often shows lower warpage in unheated chambers. Against PPSU, PEEK offers higher stiffness and temperature capability but requires higher bed and chamber setpoints. Against unfilled PEKK, PEEK exhibits a lower melting temperature but slower crystallisation; PEKK may be easier to process in some heated chambers due to lower crystallinity. Selection depends on installed printer capability: if the chamber cannot sustain 120 °C or the hot end is not rated above 400 °C, alternative PAEK or PEI filaments may be more appropriate.

Chemical processing equipment prototypes are a common application. Unfilled PEEK resists hydrolysis, steam, hot water, aliphatic hydrocarbons, chlorinated solvents, and many polar organic solvents under moderate temperature. Resistance to strong oxidising acids is limited; concentrated sulfuric acid and nitric acid attack the polymer at elevated temperatures, and mechanical stress accelerates attack under ISO 22088-3 stress-cracking protocols. Parts intended for sour gas service require rapid gas decompression testing under NORSOK M-710 or equivalent because rapid decompression can cause internal cracking at filament-welded interfaces.

Aerospace and rail interior components often use polyetheretherketone because unfilled grades achieve UL 94 V-0 flammability with low smoke density and low toxic gas emission. The filament is suitable for short-run or maintenance parts when the installed part is qualified to the same material specification as the filament resin. For flight-qualified parts, printed laminates are evaluated under FAR 25.853 or EN 45545-2 as applicable; the filament itself does not transfer a finished-part certification. Continuous service temperature ratings for unfilled PEEK are commonly reported up to 250 °C depending on load and environment, with short-term excursions to 300 °C only under low mechanical stress.

Medical device prototypes are printed from unfilled PEEK; however, the VX black grade must be confirmed against the relevant biocompatibility endpoints before use. If the resin carries USP Class VI or ISO 10993-5 data, that data applies to the raw polymer or a specific finished geometry, not automatically to a porous FFF surface. Cleaning and steam autoclave sterilisation at 121 °C or 134 °C are possible because PEEK retains stiffness through repeated autoclave cycles, but printed parts should be annealed to avoid dimensional change during the first sterilisation cycle. For implantable or prolonged skin-contact applications, a full biocompatibility plan under ISO 10993-1 is required.

In electrical connectors and semiconductor tooling, unfilled PEEK is specified for volume resistivity above 10¹⁵ Ω·cm, dielectric strength near 20 kV/mm, and low outgassing under vacuum. FFF-produced surfaces introduce roughness and microvoids that can lower dielectric strength; smooth machined surfaces are preferred for high-voltage insulation. If the black pigmentation is carbon-based, surface resistivity should be verified rather than assumed for each print profile.

Unfilled PEEK displays moderate wear rate against polished steel in dry sliding, but it is not a self-lubricating grade. For bearing and wear surfaces, unfilled VX black may require external lubrication or a mating surface of Ra 0.2 µm; carbon-fibre-filled PEEK, PEEK with PTFE, or graphite-filled grades are often selected instead. Under ISO 7148-2 or ASTM G99 pin-on-disc testing, the unfilled grade exhibits higher coefficient of friction than PTFE-filled PEEK but better machinability than highly filled grades. Specific tribological values for printed TECAFIL PEEK VX black are limited; testing on representative printed substrates is necessary.

Batch-to-batch variation in melt flow behaviour is a known issue in unfilled PEEK. Under ISO 1133-1 at 380 °C with a 5 kg load, melt volumetric flow may vary between production lots due to molecular weight differences. This variation changes extrusion pressure and layer adhesion; injection moulding grades of PEEK may not print like film-grade PEEK. Incoming lots should be checked for moisture and melt-flow behaviour before production. If no melt-flow data is supplied, a standard test coupon printed at fixed temperature and speed can reveal lot drift.

Printed PEEK blanks are often machined to final dimensions because FFF cannot hold ±0.05 mm tolerances on sealing faces. Machining generates local heating, and unfilled PEEK has relatively low thermal conductivity of 0.29 W/(m·K) under ISO 22007-2, so coolant or air blast is used to avoid gumming and thermal expansion. Precision parts are annealed before final machining to prevent later dimensional drift.

On production-scale systems with a build chamber of 300 mm × 300 mm × 300 mm or larger, the dominant bottleneck is not extrusion temperature but chamber temperature uniformity. Thermal gradients across the build volume cause differential crystallisation, with lower-crystallinity zones at the chamber door and higher crystallinity zones near the bed. This produces anisotropic shrinkage and layered parts that pass visual inspection but fail under tensile load. Mechanical data from printed coupons should be compared with machined TECAPEEK VX black resin data under the same ISO 527-2 conditioning state. For parts with wall thickness above 5 mm, solid infill creates long residence times and can increase crystallinity, embrittlement, and sink marks; sparse infill changes dielectric properties and should be avoided in electrical insulation applications unless validated.

Material handling must account for the high processing temperatures. Contact with molten PEEK or heated bed surfaces above 150 °C requires high-temperature gloves. Fumes from PEEK processing are generally low; nevertheless, local exhaust ventilation is recommended when processing above 400 °C, and workplace exposure limits should be verified under national occupational hygiene regulations. Spools should be kept away from direct sunlight and sources of moisture until dried.